This invention relates to the field of meters and particularly to meters for measuring the concentration and flow rate of fluid mixtures.
In order to control processes which utilize fluid mixtures of two materials, continuous or rapid monitoring of the concentration of the mixture and its flow rate is highly desirable. Examples of such processes include the disposal of sewage, the manufacture of paper from paper pulp, and coal water slurry transport systems for use in energy applications.
Because of the nature of many mixtures, most conventional measurement techniques are not completely satisfactory. The erosive nature of the flowing media precludes the use of devices which have moving parts or fragile components which must be immersed in the flow. Instruments which require pressure transmission through fine openings or flow through small by-pass tubes have problems with clogging caused by solid particles in the mixture.
A meter which attempts to overcome these problems is described in U.S. Pat. No. 4,423,623 by William W. Ho, Alan B. Harker, Ira B. Goldberg (also a co-inventor of the present invention), and Kwant E. Chung. This prior patent (which is hereby incorporated into the present patent by reference) utilizes microwaves to determine the concentration and velocity of the fluid mixture. The prior art meter uses a waveguide which contains the flowing mixture. Two pair of probes extend through the wall of the waveguide into the mixture to transmit and detect microwaves in the mixture. A lock-in amplifier is coupled to the probes to determine a frequency characteristic of the microwaves propagating within the waveguide section. The frequency characteristic is related to the concentration of the mixture.